Methods to treat mixtures of glycosides to obtain one or more of these glycosides in more pure form

ABSTRACT

The present invention provides methods to treat mixtures containing natural rebaudioside A (Reb A), rebaudioside B (Reb B), and rebaudioside D (Reb D), synthetic counterparts of these, and/or derivatives of the natural or synthetic embodiments obtain one or more of these glycosides in more pure form. In many embodiments, the invention can be used to process glycoside mixtures obtained at least in part from natural sources such as the  Stevia  plant. This allows, for instance, the recovery of a product including Reb A material in more pure form relative to Reb B material or Reb D material. As an alternative or in addition to recovery of the purified Reb A material, a product including Reb B material and/or Reb D material in more pure form relative to Reb A material can be obtained.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Ser.No. 61/299,160 filed 28 Jan. 2010 entitled METHODS FOR THE PURIFICATIONOF REBAUDIOSIDE B AND REBAUDIOSIDE D FROM REBAUDIOSIDE A COMPOSITIONS,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The methods of the present invention relate to treatments that resolvemixtures including rebaudioside A material, rebaudioside B material, andrebaudioside D material into more pure form(s). For example, mixtures ofrebaudioside A, B, and D can be resolved to provide the Reb A on the onehand, and/or the Reb B and/or D on the other hand, in more pure form.More specifically, the treatments use one or more crystallizationstrategies singly or in combination to purify such glycoside mixtures.

BACKGROUND

The species Stevia rebaudiana (“Stevia”) has been the subject ofconsiderable research and development efforts directed at thepurification of certain naturally occurring sweet glycosides of Steviathat have potential as non-caloric sweeteners. Sweet glycosides (alsoreferred to as steviol glycosides) that may be extracted from Steviainclude the six rebaudiosides (i.e., rebaudioside A to F), stevioside(the predominant glycoside in extracts from wild type Stevia),dulcosides, and sterebins.

Rebaudioside A (Reb A) is a sweet tasting glycoside component of Stevia,having roughly 250-450 times the sweetness of sucrose. Rebaudioside A isdesirable for use in non-caloric sweeteners because of its favorablesweetness profile, regulatory approvals, customer acceptance, andminimal bitter aftertaste. Rebaudioside B (Reb B) and D (Reb D) also aresweet tasting glycoside components of Stevia that are of interest fortheir sweetness characteristics.

The natural extracts of Stevia as well as some processed versionsthereof as well as synthetic counterparts typically include mixtures ofglycosides. It has been desirable to purify these mixtures to obtain oneor more of these glycosides in more pure form. For instance, a mixturemight include, among other ingredients, a combination of Reb A, Reb, B,and Reb D. It has been desirable in some instances to treat thesemixtures to recover a product that includes Reb A in more pure formwhile reducing the content of Reb B and/or D in the product. In otherinstances, it may be desirable to treat these mixtures to recover aproduct that includes Reb B and/or Reb D in more pure form whilereducing the content of Reb A in the product. In still other instances,these mixtures are processed to recover a combination of products. Forinstance, if a mixture is treated to recover a mixture portion that ismore pure with respect to Reb A with reduced Reb B and Reb D, anotherportion of the treated mixture generally can be recovered that has morepure Reb B and/or D and less Reb A content

Numerous methods have been reported for the purification of rebaudiosideA from crude Stevia extracts containing rebaudioside A.

Japanese Publication No. 56121454 reports a method of separatingstevioside and rebaudioside A at high purity and yield bycrystallization. In the method a mixture of stevioside and rebaudiosideA is extracted from the leaves and stalks of Stevia rebaudiana Bertoniby conventional process. The extract is dissolved in ≧70% aqueoussolution of ethanol and rebaudioside A is selectively crystallized fromthe solution.

Japanese Patent 63173531 describes a method of extracting sweetglycosides from the Stevia rebaudiana plant. The first step of theprocess is to extract a liquid solution of sweet glycosides from theStevia rebaudiana plant. Secondly, the liquid solution of sweetglycosides is passed through a non-polar porous resin and is eluted witha water-soluble organic solvent, preferably methanol. Thirdly, theeluted solution is concentrated and dried to give a powdery material.This procedure isolates a mixture of sweet glycosides, but does notisolate a single pure sweet glycoside such as rebaudioside A.

U.S. Patent Application Publication No. 2006/0083838 (Jackson et al.)reports a method of isolating and purifying rebaudioside A fromcommercially available Stevia rebaudiana starting material. The methodcomprises: (1) an ethanol (EtOH) formulation stage to formulate aselected EtOH solvent, (2) a first reflux stage using the Steviastarting material and optionally additional reflux stages usingretentate isolated from a refluxed mixture or a stirred wash mixture,(3) optionally, one or more stirred wash stages, and (4) an ethanolpurge and drying stage. In the reported method, an EtOH formulationstage is conducted in order to formulate a desired reflux solvent foruse in the reflux step(s). Typically, the reflux solvent is a mixture ofethanol and water with about 5% to 15% by volume water. The reflux stagetypically comprises providing a mixture of glycosides in the refluxsolvent and refluxing the mixture for about 1 hour, cooling the mixtureto improve the process yield, and filtering. The process furtherincludes one or more energy-intensive refluxing steps that are typicallyconducted at a temperature of about 79° C. to 80° C. for about 1 hour.The stirred wash stage typically comprises providing a mixture ofglycosides from a reflux stage and a solvent of pure ethanol, agitatingthe mixture at room temperature for about 15 minutes, and filtering. Themethod allegedly produces 100% pure, water-soluble rebaudioside A.

U.S. Pat. No. 5,962,678 (Payzant et al.) reports a method of extractingselected sweet glycosides from the Stevia rebaudiana plant. In thereported method, sweet glycosides are extracted from the Stevia plantand are processed to obtain individual components in a multi-stepprocess. First, the Stevia plant is treated to extract an aqueous liquidsolution containing mixed sweet glycosides. By using a series of ionexchange resins, the impure non-sweet glycosides are separated from themixed sweet glycosides, which are dried. These dried mixed sweetglycosides, which still contain impurities, are then dissolved in awater-soluble organic solvent such as anhydrous methanol to form asolution. The solution is refluxed and is cooled to precipitate a firstsweet glycoside component. This first sweet glycoside component, whichis typically stevioside, can be recovered by filtration and may befurther purified by the method described for the second component. Thefiltrate from the crystallization of the first precipitated sweetglycoside can be further treated to obtain a second sweet glycosidecomponent by concentrating the filtrate by heating. Upon cooling thesolution, a second sweet glycoside component precipitates which can berecovered. This second sweet glycoside component is typicallyrebaudioside A. It can be further purified by dissolving it in awater-soluble organic solvent such as methanol that may optionallycontain a small amount of water. The solution is heated, refluxed, andfinally cooled to precipitate the second sweet glycoside component at ahigher purity. The precipitate can be recovered by filtration. Thispurification process can be repeated until a final crystallized solid ofdesired purity is obtained. The method reports Rebaudioside A puritylevels of 90% or greater or 95% or greater.

U.S. Pat. No. 4,361,697 (Dobberstein et al.) reports a process forrecovering diterpene glycosides from the Stevia rebaudiana plant. Theprocess includes the steps of sequentially extracting plant materialwith a first solvent of intermediate polarity to extract plantsubstances which tend to interfere with a liquid chromatographicseparation of the glycosides, and then with a second solvent of highpolarity to extract glycosides, and chromatographically separating theextracted glycosides by introducing them onto a liquid chromatographycolumn having a packing of an oxygen-containing organic stationary phasecovalently bonded through a silicon atom to an inorganic support. Theglycosides are eluted with a solvent of polarity that is higher thanthat of the first solvent but lower than that of the second solvent.

U.S. Pat. No. 4,892,938 (Giovanetto) reports a method for recoveringsteviosides from dried plant material of Stevia rebaudiana Bertoni byextraction and purification. An extract is obtained through treatment inwater at a temperature from room temperature to about 65° C. withstirring and subsequent filtration and centrifugation. This extract istreated with calcium hydroxide, whereupon a precipitate is obtained bymeans of filtration or centrifugation. This precipitate is treated witha strongly acidic ion exchange resin and subsequently with a weaklybasic ion exchange resin, filtered and dried.

U.S. Pat. No. 4,082,858 (DuBois) reports a method for the recovery ofrebaudioside A from the leaves of Stevia rebaudiana plants. Finalpurification is achieved by liquid chromatography subsequently followedby an initial extraction with water and alkanol having from 1 to 3carbon carbons, preferably methanol. It is also disclosed that water maybe used as the initial solvent. Their preferred solvent at this stage isa liquid haloalkane having from 1 to 4 carbon atoms. The preferredsecond solvent is an alkanol having from 1 to 3 carbon atoms, while thepreferred third solvent is an alkanol having from 1 to 4 carbon atomsand optionally minor amounts of water.

U.S. Patent Application No. 2006/0134292 (Abelyan et al.) reports aprocess for recovering sweet glycosides from Stevia rebaudiana plantmaterial. The dried and powdered leaves are treated with water in thepresence of a pectinase, cellulase, and alpha-amylase. The use of suchenzymes is reported to considerably increase the extraction rate andfacilitates the next stages of purification. The resulting extract ispurified using treatment with calcium hydroxide and ultrafiltration. Thepermeate is passed through the column packed with bentonite andconcentrated to syrup state under vacuum. The treatment with ethanolallows separating the practically pure rebaudioside A from the mixture.The rebaudioside A with high purity is obtained after washing thecrystals with 88-95% of ethanol.

Other techniques include those reported, for example, in JapanesePublication Nos. 56121454; 56121455; 52062300; and 56121453 assigned toAjinomoto Company, Inc, and in Chinese Publication No. 1243835 assignedto Hailin Stevia Rebaudium Sugar.

Due to their values as non-caloric sweeteners, improvements in theavailable methods for purifying glycosides such as Reb A, Reb B, and/orReb D are desired. In particular, a method that allows for theseparation of rebaudioside A from compositions containing rebaudioside Band/or rebaudioside D is highly desirable. This would allow recovery ofa product that has more pure Reb A, a product that has more pure Reb Band/or D, or both kinds of products.

SUMMARY

The present invention provides methods to treat mixtures containingnatural rebaudiosides A, B, and D, synthetic counterparts of these,and/or derivatives of the natural or synthetic embodiments to obtain oneor more of these glycosides in more pure form. In many embodiments, theinvention can be used to process glycoside mixtures obtained at least inpart from natural sources such as the Stevia plant. This allows, forinstance, the recovery of a product including Reb A in more pure formrelative to Reb B or D. As an alternative or in addition to recovery ofthe purified Reb A, a product including Reb B and/or D in more pure formrelative to Reb A can be obtained.

Principles of the present invention allow excellent purification ofthese glycosides to be achieved at high yield. Conventionally, highpurity has been obtained at the expense of yield and vice versa.Providing methodologies that offer high levels of both yield andpurification is a significant advantage, particularly at industrialscales.

The treatments of the present invention can be used in combination withother purification strategies. In such combinations, the methods of thepresent invention can be practiced before and/or after the otherstrategies are used. In some modes of practice, such combinations can berepeated one or more additional times.

In one aspect, the present invention relates to a method of treating aglycoside mixture comprising Reb A material and at least one of Reb Bmaterial or Reb D material to help recover at least one of the Reb Amaterial, Reb B material, or Reb D material in more pure form,comprising the steps of:

-   -   a) providing a slurry comprising glycosides including at least        rebaudioside A material and at least one of Reb B material and D        material, wherein the slurry includes a solid phase and a liquid        phase;    -   b) aging the slurry at one or more elevated temperatures        independently greater than about 40° C., said aging occurring        for a time period sufficient for the solid phase to become more        pure with respect to at least one of the rebaudioside A        material, B material and D material;    -   c) filtering the heated mixture to separate the solid and liquid        phases, wherein the mixture is at a temperature of at least        40° C. during at least a portion of the filtering; and    -   d) recovering at least one glycoside in at least one of the        solid and liquid phases.

In another aspect, the present invention relates to a method of treatinga glycoside mixture comprising two or more of Reb A material, Reb Bmaterial or Reb D material to help recover at least one of the Reb Amaterial, Reb B material or Reb D material in more pure form, comprisingthe steps of:

-   -   a) providing a slurry comprising glycosides including at least        Reb A material, Reb B material, and Reb D material, wherein the        slurry includes a solid phase and a liquid phase; and    -   b) aging the slurry at one or more elevated temperatures        independently greater than about 85° C., said aging occurring        for a time period and under conditions sufficient for at least        one of (i) the solid phase to become more pure with respect to        Reb A material relative to at least one of Reb B material and D        material; and/or (ii) the liquid phase to become more pure with        respect to at least one of Reb B material and D material        relative to Reb A material.

In another aspect, the present invention relates to a method of treatinga glycoside mixture comprising two or more of Reb A material, Reb Bmaterial or Reb D material to help recover at least one of Reb Amaterial, Reb B material or Reb D material in more pure form, comprisingthe steps of:

-   -   a) providing a slurry comprising glycosides including at least        rebaudioside A material, B material and D material, wherein the        slurry includes a solid phase and a liquid phase;    -   b) aging the slurry at one or more elevated temperatures        independently greater than about 40° C., said aging occurring        for a time period sufficient for at least one of the solid phase        and/or the liquid phase to become more pure with respect to at        least one of the rebaudioside A material, B material and D        material; and    -   c) during at least a portion of the aging, agitating the heated        slurry and causing successive portions of the heated slurry to        contact a cooling surface.

In another aspect, the present invention relates to a method of treatinga glycoside mixture comprising two or more of Reb A material, Reb Bmaterial or Reb D material to help recover Reb A material in more pureform, comprising the steps of:

-   -   a) providing a first slurry comprising glycosides including at        least rebaudioside A material, B material and D material,        wherein the first slurry includes a solid phase and a liquid        phase, said liquid phase comprising a first solvent;    -   b) aging the first slurry, said aging occurring for a time        period sufficient for the solid phase to become more pure with        respect to Reb A material;    -   c) incorporating at least a portion of the solid phase obtained        in step (b) into a second slurry, wherein the second slurry        includes a solid phase and a liquid phase, said liquid phase        comprising a second solvent having a different composition than        the first solvent; and    -   d) aging the second slurry, said aging occurring for a time        period sufficient for the solid phase to become more pure with        respect to Reb A material.

In another aspect, the present invention relates to a method of treatinga glycoside mixture comprising two or more of Reb A material, Reb Bmaterial or Reb D material to help recover at least one of Reb Bmaterial or Reb D material in more pure form, comprising the steps of:

-   -   a) providing a first slurry comprising glycosides including at        least rebaudioside A material, B material and D material,        wherein the first slurry includes a solid phase and a liquid        phase, said liquid phase comprising a first solvent;    -   b) aging the first slurry, said aging occurring for a time        period sufficient for the liquid phase to become more pure with        respect to at least one of Reb B material or Reb D material;    -   c) incorporating at least a portion of the liquid phase obtained        in step (b) into a second slurry, wherein the second slurry        includes a solid phase and a liquid phase, said liquid phase        comprising a second solvent having a different composition than        the first solvent; and    -   d) aging the second slurry, said aging occurring for a time        period sufficient for the liquid phase of the second slurry to        become more pure with respect to at least one of Reb B material        or Reb D material.

In another aspect, the present invention relates to a method ofpurifying an impure rebaudioside A composition, the method comprisingthe steps of:

-   -   a) providing an impure rebaudioside A composition comprising        rebaudioside A material and at least one impurity selected from        the group consisting of rebaudioside B material and rebaudioside        D material, wherein at least a portion of the rebaudioside A        material is in a first crystalline form;    -   b) converting at least a portion of the rebaudioside A        composition from the first form into a second crystalline form;        and    -   c) converting at least a portion of the second crystalline form        of the rebaudioside A composition to a third crystalline form        said third crystalline form optionally being the same as the        first crystalline form.

In another aspect, the present invention relates to a method of treatinga glycoside mixture comprising Reb A material and at least one ofstevioside material, Reb B material or Reb D material to help recoverReb A material in more pure form, comprising the steps of:

-   -   a) providing a slurry comprising glycosides including at least        stevioside, rebaudioside A material, B material and D material,        wherein the slurry includes a solid phase and a liquid phase,        and wherein the slurry includes less than about 60 weight        percent Reb A material based on the total weight of glycosides        in the slurry and wherein the liquid phase comprises ethanol;        and    -   b) aging the slurry at one or more elevated temperatures        independently greater than about 85° C., said aging occurring        for a time period and under conditions sufficient for the solid        phase to become more pure with respect to Reb A material        relative to at least one of stevioside, Reb B material and D        material.

The purified glycoside compositions purified in accordance with thepresent invention are useful in sweetener compositions and in sweetenedfood and beverage compositions. Examples of food and beveragecompositions include carbonated beverages, non-carbonated beverages(e.g., sports drinks and dry beverage mixes), ice cream, chewing gum,candy, juices, jams, jellies, peanut butter, yogurt, or cold cereal.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is the chemical structure of rebaudioside A.

FIG. 2 is the chemical structure of rebaudioside B.

FIG. 3 is the chemical structure of rebaudioside D.

FIG. 4 a is a powder X-ray diffraction pattern for an ethanol crystalform of rebaudioside A useful in the present invention.

FIG. 4 b is a peak listing of a powder X-ray diffraction pattern for anethanol crystal form of rebaudioside A useful in the present invention.

FIG. 5 a is a powder X-ray diffraction pattern for a water crystal formof rebaudioside A useful in the present invention.

FIG. 5 b is a peak listing of a powder X-ray diffraction pattern for awater crystal form of rebaudioside A useful in the present invention.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention. All patents, pending patent applications, published patentapplications, and technical articles cited herein are incorporatedherein by reference in their respective entireties for all purposes.

The present invention provides methods for treating glycoside mixturescontaining rebaudiosides A, B, and D, derivatives of one or more ofthese, and/or synthetic counterparts of one or more of these naturaland/or derivative forms, to recover at least one of these glycosides inmore pure form relative to the starting mixture. In addition to theseglycosides, the mixtures optionally may include one or more otherglycosides. Exemplary other glycosides include the steviol glycosides,derivatives of these, or synthetic counterparts. Mixtures of Reb A, B,and D obtained from natural sources also tend to include the othersteviol glycosides.

The present invention is particularly useful for obtaining Reb Amaterial in more pure form from these mixtures relative to at least RebB material and D material. Thus, a purified composition obtained usingprinciples of the present invention may have a larger percentage of RebA material and a smaller percentage of Reb B material and/or D materialthan the starting mixture. Thus, in one aspect, the present inventionprovides methods for the removal of impurities such as rebaudioside Band rebaudioside D from impure rebaudioside A compositions.

Because the principles of the present invention can be used to separateReb A material on the one hand from Reb B material and/or D material onthe other hand, a purified composition obtained using principles of thepresent invention may have a larger percentage of Reb B material and/orD material and a smaller percentage of Reb A material than the startingmixture. Thus, in another aspect, the present invention provides methodsfor the removal of impurities such as Reb A from impure Reb B and/or Dcompositions.

As used herein, the term “rebaudioside A” or “Reb A” refers to acompound having the chemical structure shown in FIG. 1. As used herein,the term “material” used with respect to a glycoside refers to thatglycoside, derivative(s) of that glycoside, or synthetic counterpart(s)of the glycoside or its derivative(s). Thus, “Reb A material” refers toReb A, Reb A derivative(s), and/or synthetic counterpart(s) of Reb A orReb A derivative(s).

As used herein in the detailed description the term “rebaudioside B” or“Reb B” refers to a compound having the chemical structure shown in FIG.2. As used herein, “Reb B material” refers to Reb B, Reb Bderivative(s), and/or synthetic counterpart(s) of Reb B or Reb Bderivative(s).

As used herein in the detailed description the term “rebaudioside D” or“Reb D” refers to a compound having the chemical structure shown in FIG.3. As used herein, “Reb D material” refers to Reb D, Reb Dderivative(s), and/or synthetic counterpart(s) of Reb D or Reb Dderivative(s).

As used herein, a derivative of a glycoside molecule refers to aglycoside product that results from a modification of the glycoside byremoving one or more moieties, adding one or more moieties, substitutingone or more moieties for one or more other moieties, masking one or moremoieties, adding or removing unsaturation, causing unsaturation to be atanother location in the molecule, combinations of these, and the like;provided, however, that a derivative shall not include those moleculeshaving modification(s) that change (e.g., increase or decrease) thenumber of sugar units in a carbohydrate portion that was, is, or becomeslinked to the aglycone portion of the glycoside or that substitute onekind of sugar unit (e.g., a mannose unit in a representativecircumstance) for another kind of sugar unit (e.g., a glucose unit in arepresentative circumstance). Derivatives do include modifications tothe sugar unit(s), if any, that are present if the type and number ofsuch sugar units does not change as a result of the modification.

For example, adding a sugar moiety to the Reb A carbohydrate portionthat is linked to the aglycone via the natural ester linkage convertsthe Reb A to Reb D. The carbohydrate chain there is increased from onesugar unit to two sugar units. Such a modification yields Reb D, not aderivative of Reb A. Similarly, removing such sugar moiety from Reb Ayields Reb B rather than a Reb A derivative where there is no longer acarbohydrate chain at such location.

A synthetic counterpart refers to a molecule that is substantially thesame as a natural glycoside or a derivative of a natural glycosideexcept the counterpart is obtained via chemical synthesis rather thanbeing obtained from a natural source. The stereochemistry of syntheticmolecules may be the same or different than that of the naturalcounterpart. Where there are multiple chiral centers, some of these maybe the same while others are different as between the synthetic andnatural counterparts. The glycosides of the mixture can be provided in avariety of morphological and physical forms. For instance, theglycosides independently can be provided in crystalline, partiallycrystalline, and/or amorphous forms. Glycosides can be supplied in dryform or can be supplied as a constituent of a paste, slurry, or thelike. In other instances, the glycosides can be at least partiallydissolved and supplied in solutions, gels or the like.

In one mode of practice, at least a portion of the glycosides arecrystalline and are provided in an alcohol crystalline form. Generally,this means that a glycoside has been crystallized in a liquid carrierincluding at least 80%, even at least 90%, even at least 95%, or even atleast substantially 100% of one alcohol such as methanol, ethanol,ispropanol, n-butanol, combinations of these, and the like. Water is anexemplary co-solvent in such modes of practice. Aqueous alcoholsdesirably include at least about 80 weight percent, even at least about90 weight percent, or even at least about 95 weight percent ofalcohol(s). In some embodiments the ethanol that is used to prepare theslurry comprises 190 proof ethanol (i.e., 93-95 weight percent ethanol).Other grades of ethanol (e.g., 180 proof or 200 proof ethanol) may alsobe useful.

Ethanol crystalline forms are preferred, particularly in embodiments inwhich it is desired to obtain Reb A material in more pure form relativeto Reb B material and Reb D material that might be in a startingmixture. Data has shown that the purity of the Reb A is higher when thetreatment is applied to a glycoside mixture in which at least a portionof the Reb A is in an ethanol crystalline form. In other modes ofpractice, at least a portion of the glycosides are provided in a watercrystalline form. Generally, this means that a glycoside has beencrystallized in a liquid carrier including at least 80%, even at least90%, even at least 95%, or even at least substantially 100% water.

Non-limiting examples of useful ethanol and water crystal foil is aredescribed in commonly assigned U.S. Provisional Application Ser. No.61/168,072, filed Apr. 9, 2009, and entitled “SWEETENER COMPOSITIONCOMPRISING HIGH SOLUBILITY FORM OF REBAUDIOSIDE A AND METHOD OF MAKING”and its published counterpart PCT Pub. No. WO 2010/118218A1, each ofthese disclosures being independently incorporated herein by referencein its respective entirety.

The crystalline form of a glycoside can differ depending upon the natureof the liquid carrier in which the glycoside was crystallized. Forinstance, the alcohol crystalline form of Reb A differs from the watercrystalline faun of Reb A. The ethanol crystal form may becharacterized, for example, by having an X-ray diffraction pattern asshown in FIG. 4 a. The water crystal form may be characterized, forexample, by having an X-ray diffraction pattern as shown in FIG. 5 a.

In some modes of practice, the principles of the present invention areapplied to successive crystalline forms of the glycoside(s). Thus, theprinciples of the present invention may be applied to glycosides in afirst stage of processing in which at least a portion of the glycosidesare in a first crystalline form. By way of example, at least a portionof the glycosides are in an ethanol crystalline form in such firststage. In a subsequent processing stage, the principles of the presentinvention are then applied to the glycosides when at least a portion ofthe glycosides are in a second crystalline form. By way of example, atleast a portion of the glycosides are in a water crystalline form insuch subsequent stage. The first and/or second stages may be repeated asdesired.

Those modes of practice in which the principles of the present inventionare applied to successive crystalline forms of the glycoside(s) arereferred to herein as form transition purification. This terminologyindicates that the crystalline form of the glycoside(s) undergoes atleast one crystalline form transition during the course of thetreatment. Data has shown that the purity of a glycoside product such asReb A is enhanced when incorporating form transition strategies into apurification treatment. Without wishing to be bound, it is believed thatthe enhancement arises because a crystalline glycoside dissolves in aliquid carrier and then re-crystallizes in the new crystalline form inthe course of the transition. Hence, any impurities or other ingredientsincorporated into a crystalline lattice are more easily released and/orseparated as the crystal dissolves as compared to a mechanism in whichthe crystalline transition were to occur from one solid phase directlyto another solid phase.

Exemplary modes of practice incorporating form transition purificationare described further below including in the Examples.

According to the present invention, the glycoside mixture to be treatedis incorporated into a slurry including at least one solid phase and atleast one liquid phase. The solid phase(s) can be amorphous and/orcrystalline. The slurry generally is obtained from ingredients thatinclude at least the mixture to be treated and a suitable liquidcarrier.

The amount of the glycoside mixture incorporated into the slurry canvary over a wide range. The concentration of the glycoside mixture inthe slurry may be varied to affect the rate of purification. Forinstance, the removal of rebaudioside B and rebaudioside D from animpure rebaudioside A composition is impacted by this concentration.Generally speaking, as the concentration of the slurry increases (i.e.,higher dissolved solids) the rate of separation of Reb A material on theone hand from Reb B material and Reb D material on the other hand tendsto decrease. Having too much solids content also can make it moredifficult to stir and filter the slurry during the course of thetreatment. Yet, throughput, cost, and efficiency are reduced if thesolids content is too low. Balancing such practical concerns,illustrative slurry embodiments include from about 5 weight percent toabout 50 weight percent, preferably about 10 weight percent to about 40weight percent, more preferably about 15 weight percent to about 30weight percent of the glycosides based on the total weight of theslurry.

The slurry is heated to at least one elevated temperature above ambienttemperature and is allowed to age at the elevated temperature(s). Theaging occurs for a time period sufficient for at least one of (i) thecrystalline phase to become more pure with respect to at least one ofthe glycosides (such as Reb A material) and/or (ii) the liquid phase tobecome more pure with respect to at least one of the other glycosides(such as at least one of Reb B material or D material). Longer agingtends to provide more purification. Thus, longer aging of the slurryincreases the extent of removal of rebaudioside B material andrebaudioside D material from an impure rebaudioside A composition. Theduration of aging is mainly subject to practical limits. For instance,after some duration, the amount of further purification that occursslows down too much to be economically practical. Balancing suchconcerns in some embodiments, the slurry is aged for a period of timeranging from about 1 hour or greater, for example, from about 1 hour toabout 24 hours. In a preferred aspect, the slurry is aged for a periodof time ranging from about 3 to about 8 hours, or even about 4 to about6 hours.

The liquid carrier desirably includes water, an alcohol, or acombination of these. Exemplary alcohols include methanol, ethanol,isopropanol, n-propanol, n-butanol, isobutanol, t-butanol, combinationsof these, and the like. The alcohol(s) may be aqueous as discussedherein. In some embodiments the ethanol that is used to prepare theslurry comprises 190 proof ethanol (i.e., 93-95 weight percent ethanol).Other grades of ethanol (e.g., 180 proof or 200 proof ethanol) may alsobe useful.

The treatment may occur at a wide range of elevated temperatures.Desirably, boiling and reflux of the liquid carrier are avoided. Heatincreases the rate and extent of separation of rebaudioside B materialand rebaudioside D material from rebaudioside A material. Withoutwishing to be bound by theory, it is believed that one or more of theglycosides undergo conformational or other transformations that favorseparation. In such embodiments, the slurry is heated at a temperatureof at least about 40° C. to, preferably at least about 50° C., morepreferably at least about 70° C., and even more preferably at leastabout 95° C. Heating desirably occurs up to a temperature of about 200°C., preferably 150° C., more preferably 120° C. In one mode of practice,heating at 100° C. is suitable.

When the mixture is well mixed, the bulk temperature generally isuniform throughout the mixture. In such well-mixed mixtures, the bulktemperature desirably is in such temperature ranges. When the mixture isnot well-mixed such that a temperature gradient exists, then at least aportion, desirably at least about 5 volume percent, more desirably atleast about 30 volume percent, more desirably at least about 50 volumepercent of the mixture has temperature(s) in such temperature ranges.

The treatment may occur under a range of pressures. For instance, thetreatment may occur under ambient pressure or elevated pressure(s)greater than ambient pressure. Elevated pressures allow the slurry to beheated at higher temperatures while staying below the boiling point ofthe liquid at the elevated pressure. Exemplary absolute pressures rangefrom ambient pressure to about 30 atm, even about 1.1 atm to about 30atm, preferably about 1.1 atm to about 15 atm, more preferably about 1.1atm to about 10 atm, and even more preferably from about 1.1 atm toabout 5 atm. In some modes of practice using liquid carriers comprisingat least 90 weight percent ethanol in water, using a pressure of about 3atm is suitable. Elevated pressures allow the use of higher temperaturesin those embodiments in which it is desirable that the pressure ishigher than the vapor pressure of the solvent at the desiredtemperature. This is desirable in that higher temperatures generallylead to better resolution among glycosides. For example, highertemperatures generally provide better resolution between Reb A materialon one hand and Reb B material and D material on the other hand.

In some embodiments the slurry is agitated during treatment. Agitationgenerally increases the degree of purification. For example, agitationof a slurry comprising Reb A material, B material, and D materialincreases the rate and extent of separation of rebaudioside B materialand rebaudioside D material from the rebaudioside A material. Typicallyagitation comprises, for example, mixing at high speed (e.g., 200 rpm)with an impeller in a baffled mixing vessel (e.g., a 5-liter baffledmixing vessel).

As the slurry is aged, the glycoside components are selectivelypartitioned between the solid and liquid phases. In the case of Reb Amaterial, B material and D material, Reb A material tends to be morefavored in the solid phase while Reb B material and D material are morefavored in the liquid phase. This means more pure Reb A material isobtained in the solid phase, while more pure Reb B material and Dmaterial are in the liquid phase. The resultant solid phase alsocomprises crystalline content.

The two phases are easily separated by a variety of techniques,including filtration, to recover the desired purified material. If pureReb A material is desired, the crystals can be filtered, washed, dried,further processed, or the like. If Reb B material and/or D material aredesired, the liquid can be processed to recover the Reb B-material and Dmaterial as a dried product, a dispersion, a solution, or the like. Avariety of drying techniques may be used including spray drying, ovendrying, vacuum drying, combinations of these, and the like.

In preferred embodiments, the solid and liquid phases resulting from thetreatment are separated by filtering. Desirably, the product mixture isat a temperature of at least about 50° C., preferably at least about 70°C. during at least a portion of the filtering. Hot filtrationadvantageously enhances separation of Reb B material and Reb D materialfrom Reb A material in mixtures that include Reb A material, B material,and D material.

Without wishing to be bound, it is believed that separation is morefavored at higher temperatures at least in part due to factors includingconformational changes as well as solubility differences that are afunction of temperature. At room temperature, the solubility of Reb B ina 94 weight percent ethanol solution saturated with Reb A is about 0.3 gper 100 g of solvent, and the solubility of Reb D is about 0.01 g per100 g. At 100° C., concentrations of Reb D as high as 0.2 g/100 g areobserved, and concentrations of Reb B as high as 0.5 g/100 g areobserved. The solubility of Reb A in 94 wt % ethanol varies to a muchsmaller extent.

Aging the slurry at high temperatures thus increases the concentrationof Reb B material and Reb D material in solution, and correspondinglydecreases the Reb B material and Reb D material amounts in the solidphase. Hot filtration more easily allows the separation of Reb Bmaterial and Reb D material from Reb A material by separating the solidsand liquid while maintaining the higher solubility of Reb B material andReb D material. In contrast, cold filtering might risk precipitation ofReb B material and Reb D material such that the Reb B material and Reb Dmaterial concentrations in the liquid are closer to the room temperaturesolubilities. This can cause more Reb B material and D material to be inthe solid phase, leading to less pure Reb A material in the solid phase.Thus, cold filtering can undermine purification gains obtained earlierin the treatment. If it is desired to cool prior to filtration, theslurry may be cooled only to the extent necessary. In one instance,cooling from 100° C. to 70° C. prior to filtration maintains thepurification of the method while reducing the risks associated withfiltration.

Although not wishing to be bound by theory, it is believed thatpurification occurs at least in part via solvent mediatedcrystallization due to the presence of both solid and liquid phases. Ina slurry where solid and liquid phases are present, crystallization anddissolution occur simultaneously. This means that, at any one point intime, it might be true that only a portion of the glycoside(s) are in acrystal phase, while the remainder tends to be dissolved in the liquidphase. It is believed, however, that substantially all of the availableglycoside(s) participate in dissolution and crystallization such thatdiffering portions of the glycosides are continuously precipitating intoone or more insoluble states while other portions are being convertedinto one or more soluble states. In short, while only some of theglycoside might be in one phase or the other at any one point in time,substantially all of the glycoside crystallizes and dissolves repeatedlyover time. As successive portions are dissolved and crystallized, thepartitioning between the phases, and hence the purity, becomes enhanced.The process is dynamic and can lead to changes in purity and shape overtime.

In some embodiments, the dissolution and the crystallization occurgenerally at substantially equal rates such that there is very little ifany net change in the macroscopic partition between the two phases. Thatis, molecules in the crystalline phase dissolve and molecules in theliquid phase can crystallize at substantially equal rates.

In some embodiments, particularly when the mixture is agitated duringheat treatment, it is desirable if the heat treatment occurs in thepresence of one or more cooling surfaces that are at a temperature thatis less than the bulk temperature of the mixture being treated. Thus, asthe mixture is agitated and thereby mixed during the course of the heattreatment, successive portions of the mixture will be in contact withthe cooling surface(s). Even though mixing causes the bulk of themixture to generally be at a uniform bulk temperature, heating themixture in the presence of such cooling surface(s) has been found toenhance the purification. In contrast, merely subjecting the heatedmixture to repeated cycles of heating and cooling has not been observedto provide the same purification enhancement.

Without wishing to be bound, a potential theory to explain the benefitof heating in the presence of a cooling surface can be suggested. Thepresence of both hot and cold surfaces in the mixture tends to favorcrystallization near the cold surfaces but dissolution near the hotsurfaces or in the hotter bulk mixture. By maintaining a cold surface inthe mixture, crystallization and dissolution happen more frequently ascrystals are convected from the cold zone to the hot zone, leading tohigher purification at least for crystalline starting materials. Thepresence of both hot and cold surfaces also leads to larger particlesizes when using either crystalline or amorphous starting materialsbecause smaller particles more rapidly dissolve due to a higher surfacearea to volume ratio. The higher purification may alternatively be dueto the decreased fraction of small crystals in the mixture. It is alsobelieved that using cold surfaces in the hot mixture may also increasethe rate of purification for both amorphous and crystalline startingmaterials.

Generally, the cooling surface(s) are at one or more temperature(s)below about 40° C., preferably about 35° C. or less, even about 30° C.or less. Cooling surfaces can be provided in a variety of ways. In oneembodiment, a cooling surface is provided by the surface of a coil thatis immersed in the mixture and through which a cooling fluid flows. Insuch a mode of practice, the fluid might enter the immersed portion ofthe coil at an initial temperature, e.g., about 30° C. or less, evenabout 20° C. or less or even about 15° C. or less and exit the immersedportion of the coil at a moderately higher temperature due to heattransfer, such as about 5° C. or more warmer, even 10° C. or morewanner, or even 15° C. or more warmer. In another embodiment, thecooling surface is provided by an external heat exchanger, through whicha portion of the slurry, drawn from and returning to the heating vessel,is circulated.

In a preferred embodiment of this aspect, the slurry can be heated undergreater than ambient pressure as described above in order to more easilyallow the treatment to occur at higher temperatures. It has been foundthat carrying out the treatment at higher temperatures under elevatedpressure enhances the resolution between Reb A on the one hand and Reb Band D on the other hand.

Typically, the glycoside mixture that is used as a starting material inthe method of the invention comprises a major amount of rebaudioside Amaterial. A major amount means at least about 20 weight percent.Typically, the glycoside mixture may include from about 20 weightpercent to about 96, preferably about 30 to about 96, more preferablyabout 40 to about 96 weight percent of Reb A material based on the totalweight of glycosides. The total amount of both rebaudioside B materialand rebaudioside D material in the mixture can vary. In manyembodiments, the total amount of Reb B material and D material is up toabout 6 weight percent based on the total weight of the glycosides. Forexample, in some embodiments the mixture comprises about 90 weightpercent to about 96 weight percent rebaudioside A; about 1 weightpercent to 4 weight percent rebaudioside B; and about 1 weight percentto about 4 weight percent rebaudioside D. A crystalline product obtainedusing the principles of the present invention may include at least about80 weight percent, even at least about 90 weight percent, or even atleast about 96 weight percent of Reb A.

It is quite advantageous that the present invention can be used toenhance the purity of Reb A material within glycoside mixturescontaining about 60 weight percent or less, even 45 weight percent orless, or even 30 weight percent or less of Reb A material, particularlywhen the amount of stevioside material in such mixtures is at leastabout 10 weight percent of the total glycosides, or even at least about20 weight percent of the total glycosides, or even greater than theamount of Reb A material in some embodiments. Reb A material in suchcompositions may be crystalline or amorphous, but often is at leastpartially amorphous. In many conventional processes when Reb A materialis present in glycoside mixtures at such lower content levels, Reb Amaterial is too soluble in solvents such as water or ethanol to beadequately crystallized and purified. Desirably, the liquid phase of theslurry(ies) used in such embodiments includes ethanol, desirably atleast about 80 weight percent ethanol, or even at least about 90 weightpercent ethanol, or even at least about 95 weight percent of ethanolbased on the total weight of solvent incorporated into the slurry.

Without wishing to be bound, it is believed that such mixtures,particularly when obtained from natural sources, tend to includerelatively greater amounts of stevioside material. The steviosidematerial tends to solubilize the Reb A material. The solvent mediatedcrystallization treatment of the invention, optionally in combinationwith transition crystallization, is able to selectively partition Reb Amaterial into a crystalline phase notwithstanding the solubilizingeffects of stevioside material that otherwise would be expected to be atechnical obstacle based on conventional experiences. Without wishing tobe bound by theory, it is believed that elevated temperatures,particularly at 85° C. or higher, preferably 90° C. or higher, morepreferably 100° C. or higher induce conformational changes in thesteviol glycosides that promote crystallization of Reb A material evenin such an unfavorable context.

It is also quite advantageous that the present invention can be used toboost the purity or Reb A material that is already highly pure. Forinstance, some conventional processes might be able to produce crystalsthat include about 90 weight percent to about 95 weight percent Reb Amaterial. While such crystals are highly pure with respect to Reb Amaterial pursuant to many applicable standards, there are otherstandards in which even more pure Reb A material is desired. The presentinvention can be applied to such crystals to boost the Reb A purity toas much as 96 weight percent, even 96 weight percent to 99 weightpercent.

In one preferred embodiment of the method of the invention, a 30 weightpercent slurry of impure rebaudioside A in 190 proof ethanol is heatedto 70° C. and is held for about one hour with agitation. Following this,a retentate product including rebaudioside A crystals is recovered byfiltration, and the retentate is washed with 190 proof ethanol (e.g.,about 2 cake weights of solvent). The method results in the removal ofabout 30% rebaudioside B and about 50% rebaudioside D from the impurerebaudioside A composition. The yield of rebaudioside A is typicallyabout 95 weight percent.

In another preferred embodiment of the method of the invention, a 30weight percent slurry of impure rebaudioside A in 190 proof ethanol isheated to 70° C. and is held for about 24 hours with agitation.Following this, a retentate product including the rebaudioside Acrystals is recovered by filtration and the retentate is washed with 190proof ethanol (e.g., about 2 cake weights of solvent). The methodresults in the removal of about 50% rebaudioside B and about 50%rebaudioside D from the impure rebaudioside A composition. The yield ofrebaudioside A is typically about 95 weight percent.

A representative purified rebaudioside A composition typically compriseabout 97 weight percent or greater rebaudioside A material; about 2weight percent or less rebaudioside B material; and about 2 weightpercent or less rebaudioside D material. Other components that may beincluded in the purified rebaudioside A composition include, forexample, stevioside material, rebaudioside C material, and rebaudiosideF material.

Particularly preferred aspects of the present invention involveseparating (also referred to as resolving) Reb A material on the onehand from Reb B material and/or D material on the other hand. In onesuch aspect, the present invention provides a method of purifying animpure rebaudioside A composition using effects that are believed tooccur at least in part to solvent mediated crystallization. The impurerebaudioside A composition comprises at least one impurity selected fromrebaudioside B material and rebaudioside D material. Desirably, at leastthe Reb A material is in an ethanol crystalline form.

In other embodiments, the Reb A material may be in other crystal formsand/or may be amorphous. The method comprises the steps of: (a)providing an impure rebaudioside A composition comprising rebaudioside Amaterial and at least one impurity selected from rebaudioside B materialand rebaudioside D material; (b) preparing a slurry of the impurerebaudioside A composition in a suitable liquid carrier such as ethanol;(c) aging the slurry for a period of time of about 1 hour or greater;(d) optionally, heating the slurry during at least a portion of theaging such as to a temperature of about 45° C. to about 100° C.; (e)optionally, agitating the slurry during at least a portion of the aging;and (f) after the aging step, filtering the slurry to collect thecrystals (retentate) including the purified Reb A material, and washingthe retentate to provide a purified rebaudioside A composition. In thepurified rebaudioside A composition at least a portion of at least oneof the impurities has been reduced as compared to the impurerebaudioside A composition.

In some aspects, the invention provides a method of purifying glycosidemixtures, such as an impure rebaudioside A composition, thatincorporates form transition purification. In such embodiments, aglycoside mixture is provided wherein at least one glycoside is in afirst crystalline form. For example, an impure rebaudioside Acomposition may be provided that comprises rebaudioside A material andat least one impurity selected from the group consisting of rebaudiosideB material and rebaudioside D material. At least the Reb A material isin a first crystalline form such as an ethanol crystalline form. Theethanol crystalline form can be aged in a slurry as described above toenhance purity of the crystals with respect to Reb A material. Themixture is then treated to convert the glycoside into a secondcrystalline form. For example this may involve converting therebaudioside A material from an ethanol crystalline form into a watercrystalline form. The water crystalline form can be aged in a slurry asdescribed above to enhance purity of the crystals with respect to Reb Amaterial. Then, the water crystalline form of the rebaudioside Amaterial can be converted from the water crystalline form to an ethanolcrystalline form. Again, this form can be aged in a slurry as describedabove to enhance purity. This series of conversions helps to provide apurified rebaudioside A composition having a reduced amount of at leastone impurity selected from rebaudioside B material and rebaudioside Dmaterial.

In some embodiments, the step of converting the ethanol crystal form tothe water crystal form comprises: (a) combining the rebaudioside Acomposition with water to form a water-based slurry; and (b) allowingthe water-based slurry to stand for a period of time sufficient toconvert the ethanol crystalline form to a water crystalline form. Thewater crystalline form may be described as a four-hydrate polymorph ofrebaudioside A. In some embodiments, the step of converting the watercrystal form to the ethanol crystal form comprises: (a) combining therebaudioside A composition with ethanol to form an ethanol-based slurry;and (b) allowing the ethanol-based slurry to stand for a period of timesufficient to convert the water crystal form to an ethanol crystallineform. The solids content, solvent characters, agitation, temperatures,pressures can be selected as described above with respect to the solventmediated crystallization techniques. However, the ethanol used toconvert the water form to the ethanol form typically comprises greaterthan about 93 weight percent ethanol although other concentrations mayalso be used.

The form transition purification results in the removal of rebaudiosideB material, rebaudioside D material, or both from the impurerebaudioside A composition (i.e., the starting material). In someembodiments, the form transition results in the removal of up to about50% of the rebaudioside B and up to about 95% of the rebaudioside D thatwas present in the impure rebaudioside A composition.

The principles of the present invention can be used in combination withother purification strategies. For example, PCT Pub. No. WO2008/091547A2 describes a method of purifying glycosides such as Reb Ausing solvent/antisolvent/solvent techniques. The present invention canbe used prior to and/or after such solvent/antisolvent/solventtechniques to obtain purified Reb A even more effectively and/orefficiently. PCT Pub. No. WO 2008/091547A2 is incorporated herein byreference in its entirety for all purposes.

The invention will now be described with reference to the followingnon-limiting examples.

EXAMPLE 1

Each of three samples of glycoside material containing the 90%, 95%, 92%Reb A %, respectively, and 2.9%, 0.1%, 1.0% Reb D, respectively, and0.07%, 3.0%, 1.4% Reb B, respectively, in the ethanol crystalline formswas mixed with water to form a slurry of 13% solids in water. The slurrywas agitated overnight at room temperature with a magnetic stir bar andstir plate, with sufficient agitation to keep all solid materialsuspended. After aging overnight, the material was filtered. Thematerial contained 93%, 95%, and 95% Reb A, respectively; 2.4%, 0%, and0.6% Reb D, respectively; and 0.5%, 3.9%, and 2.5% Reb B, respectively.The material recovered in the solid phase from each treatment was 88%,98%, and 98%, respectively, of the total material fed to the process.The filtrate was dried in a vacuum oven, and contained 73%, 79%, 72% RebA, respectively; 9.6%, 1.8%, 8.4% Reb D, respectively; and 0.4%, 3.7%,0.5% Reb B, respectively.

EXAMPLE 2

Each of the three materials produced in Example 1 was slurried in pureethanol in a slurry of 3.3%, 8.8%, 6.0% solids, respectively, andagitated overnight at room temperature. After the secondary aging, thematerial was again filtered, washed with 200-proof ethanol, and dried.Each filtered product contained 99%, 98%, 98% Reb A, respectively, 1.1%,0.0%, 0.1% Reb D, respectively, and 0.1%, 1.3%, 1.0% Reb B,respectively. The overall yield of material in the solid phase,including the step in Example 1, was 64%, 83%, and 73%, respectively.The filtrate was dried in a vacuum oven, and contained 86%, 49%, 74% RebA, respectively; 3.0%, 0.36%, 2.6% Reb D, respectively; and 1.6%, 19%,11% Reb B, respectively.

EXAMPLE 3

Each of the three materials produced in Example 1 was slurried in190-proof ethanol in a slurry of 6.9%, 4.9%, 7.2% solids, respectively,and agitated overnight at room temperature. After the secondary aging,the material was again filtered, washed with 190-proof ethanol, anddried. Each product contained 99%, 99%, 99% Reb A, respectively, 0.0%,0.3%, 0.3% Reb D, respectively, and 1.0%, 0.1%, 0.6% Reb B,respectively. The overall yield of material recovered in the solidphase, including the processing in Example 1, was 68%, 45%, 71%,respectively. The filtrate was dried in a vacuum oven, and contained74%, 81%, 73% Reb A, respectively; 10%, 2.3%, 9.7% Reb D, respectively;and 0.5%, 3.5%, 0.5% Reb B, respectively.

EXAMPLE 4

Each of three samples of glycoside material containing the 90%, 95%, 92%Reb A %, respectively, and 2.9%, 0.1%, 1.0% Reb D, respectively, and0.07%, 3.0%, 1.4% Reb B, respectively, in the ethanol crystalline formswere processed as in Example 1. The collected solid material afterprocessing contained 97%, 95%, 95% Reb A, respectively; 1.1%, 0%, 0.65%Reb D, respectively; and 0.9%, 3.9%, 2.9% Reb B, respectively. Each ofthe three collected solid materials was slurried in pure methanol at5.1%, 6.0%, 5.3% solids, respectively, and agitated overnight at roomtemperature. After the secondary aging, the material was again filtered,washed with pure methanol, and dried. The product contained 99%, 99%,99% Reb A, respectively, 0.2%, 0.0%, 0.2% Reb D, respectively, and 0.2%,1.3%, 0.7% Reb B, respectively. The overall yield of material recoveredin the solid phase, including the first step processing in water, was41%, 64%, 58%. The filtrate was collected and dried in a vacuum oven,and contained 83%, 79%, 72% Reb A, respectively; 6.5%, 2.7%, 9.6% Reb D,respectively; and 0.5%, 4.0%, 0.4% Reb B, respectively.

EXAMPLE 5

Material containing ethanol crystalline forms of 93.4% Reb A, 2.4% RebD, and 1.5% Reb B was mixed with 190-proof ethanol to produce a slurrycontaining 10% solids. The slurry was agitated at room temperature.After one hour, a sample of the material was filtered, washed with190-proof ethanol, and dried. The sample contained 96% Reb A, 1.5% RebD, and 1.6% Reb B. 89% of the glycoside material in the sample wasrecovered as a solid phase. The remaining slurry was held overnight,then filtered, washed with 190-proof ethanol, and dried. After anadditional ˜24 hours in the slurry, the crystalline product from theremaining slurry contained 96% Reb A, 1.4% Reb D, and 1.4% Reb B, and89% of the glycoside material of the remaining slurry was recovered as asolid phase. The filtrate was collected and dried in a vacuum oven, andcontained 83% Reb A, 10.4% Reb D, and 4.9% Reb B.

EXAMPLE 6

Material containing ethanol crystalline fauns of 93.4% Reb A, 2.4% RebD, and 1.5% Reb B was mixed with 190-proof ethanol to produce a slurrycontaining 30% solids. The slurry was heated to 70° C. and agitated.After one hour, a sample was filtered at 70° C. washed with 190-proofethanol, and dried. The sample contained 96% Reb A, 1.8% Reb D, and 1.7%Reb B. 95% of the glycoside material in the sample was recovered as asolid phase. The filtrate was collected and dried in a vacuum oven, andcontained 87% Reb A, 7.0% Reb D, and 3.9% Reb B. The slurry remainingafter this sampling was held overnight, then filtered, washed with190-proof ethanol, and dried. After an additional ˜24 hours in theslurry, the crystalline product of the remaining contained 98% Reb A,1.3% Reb D, and 0.4% Reb B, and 95% of the glycoside material wasrecovered from the remaining slurry as a solid phase

EXAMPLE 7

Material containing ethanol crystalline forms of 93.4% Reb A, 2.4% RebD, and 1.5% Reb B was mixed with pure ethanol to produce a slurrycontaining 30% solids. The slurry was heated to 70° C. and agitated.After one hour, a sample was filtered at 70° C., washed with pureethanol, and dried. The sample contained 95% Reb A, 2.3% Reb D, and 1.5%Reb B, and 97% of the glycoside material in the sample was recovered asa solid phase. The filtrate was collected and dried in a vacuum oven,and contained 73% Reb A, 7.7% Reb D, and 17% Reb B. The remaining slurrywas held overnight, then filtered at 70° C., washed with 190-proofethanol, and dried. After an additional ˜24 hours in the slurry, thecrystalline product of the remaining slurry contained 96% Reb A, 2.1%Reb D, and 1.3% Reb B, and 96% of the glycoside material of theremaining slurry was recovered as a solid phase.

EXAMPLE 8

58 g of amorphous steviol glycosides were placed in 94 wt % ethanol toproduce a slurry with 20% by weight steviol glycosides. The slurry wasplaced in a 500 ml pressure vessel at 20 psig with an agitator and acooling loop with 58 cm² surface area. The cooling loop was a simpleU-loop of stainless steel, about 40 cm in total length, slightly offsetfrom the center of the vessel to accommodate an agitator. The vessel waspurged with nitrogen. The slurry was then heated to a bulk temperatureof 100° C. over 1 hour and held at 100° C. for 2 hours. Water at 15° C.was fed to the cooling loop at 60 ml/min. The cooling water exited thecooling loop at 25° C. The pressure vessel was agitated at 180 rpm.After the two hour hold at 100°, the mixture was cooled to 70° C. over30 minutes, filtered in a Buchner funnel at 70° C., and washed with 57 gof pure ethanol in the Buchner funnel. The solids were collected, dried,and analyzed by HPLC. 12 g of material was produced.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B wt %glycosides 1.1 35.0 39.5 1.2 7.9 0.4 3.4 0.1 of Feed Material by HPLC wt% glycosides 0.2 91.3  0.5 1.1 5.1 0.2 — 0.1 of solids by HPLC

EXAMPLE 9

91 g of amorphous steviol glycosides were placed in 100% ethanol toproduce a slurry with 30% by weight steviol glycosides. The slurry wasplaced in a pressure vessel according to Example 8 at 20 psig. Thevessel was purged with nitrogen, then the mixture was heated to a bulktemperature of 100° C. over 1 hour and held at 100° C. for 2 hours, withflow of 60 ml/min of water at 15° C. inlet through the cooling loop withagitation of 180 rpm. The outlet temp of the cooling water was 25° C.The mixture was then cooled to 70° C. over 30 minutes, filtered at 70°C. in a Buchner funnel, and washed with 63 g of pure ethanol in theBuchner funnel. The solids were dried, and analyzed by HPLC. 8 g ofmaterial was produced.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides 2.4  22.3  19.2 0.9  4.9  0.6  2.3 13.7 5.7  of Feed Materialby HPLC wt % glycosides of 0.14 83.14   0.26 1.08 5.05 0.38 —   3.260.19 solids by HPLC

EXAMPLE 10

59 g of ethanol crystalline form Steviol glycosides were placed in 94 wt% ethanol to produce a slurry with 19% by weight steviol glycosides. Theslurry was placed in a pressure vessel according to Example 8 at 20psig. The vessel was purged with nitrogen. The slurry was then heated toa bulk temperature of 100° C. over 1 hour and held at 100° C. for 6hours with a flow of 60 ml/min of water at 15° C. inlet through thecooling loop with agitation at 180 rpm. The outlet temp of the coolingwater was 25°. The mixture was then cooled to 70° C. over 30 minutes,filtered at 70° C. and washed with 107 g of pure ethanol. The solidswere collected, dried, and analyzed by HPLC. 37 g of material wasrecovered as product. The filtrate was collected, dried in a vacuumoven, and analyzed by HPLC.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides 2.8 94.7 0.1 0.2 0.0 — — 0.8 — of Feed Material by HPLC wt %glycosides of 1.7 96.9 — 0.1 — — — 0.6 — solids by HPLC wt % glycosidesof 8.0 86.4 0.7 0.3 0.1 — — 3.7 — filtrate by HPLC

EXAMPLE 11

59 g of amorphous Steviol glycosides were placed in 94 wt % ethanol toproduce a slurry with 19% by weight steviol glycosides. The slurry wasplaced in a pressure vessel according to Example 8 at 20 psig. Thevessel was purged with nitrogen. The slurry was then heated to a bulktemperature of 100° C. over 1 hour and held at 100° C. for 2 hours witha flow of 60 ml/min of water at 15° C. inlet through the cooling loopand agitation at 180 rpm. The outlet temp of the cooling water was 25°C. The mixture was then cooled to 70° C. over 30 minutes, filtered at70° C., and washed with 133 g of pure ethanol in a Buchner funnel. Thesolids were collected and analyzed by HPLC. 35 g of material wasproduced. The filtrate was collected, dried in a vacuum oven, andanalyzed by HPLC.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides of 2.3 81.6  7.1 0.6 2.3 0.1 — 2.1 0.2 Feed Material by HPLCwt % glycosides of 1.7 92.6  1.5 1.2 0.4 — — 1.0 — solids by HPLC wt %glycosides of 3.4 42.6 30.6 1.1 5.1 1.0 — 8.3 2.7 solids by HPLC

EXAMPLE 12

60 g of amorphous Steviol glycosides were placed in pure ethanol toproduce a slurry with 19% by weight steviol glycosides. The slurry wasplaced in a pressure vessel according to Example 8 at 20 psig. Thevessel was purged with nitrogen. The slurry was then heated to a bulktemperature of 100° C. over 1 hour and held at 100° C. for 2 hours withagitation at 180 rpm and with flow of 60 ml/min of water at 15° C. inletthrough the cooling loop. The outlet temp of the cooling water was 25°C. The mixture was then cooled to 70° C., filtered at 70° ° C., andwashed with 148 g of pure ethanol. The solids were collected andanalyzed by HPLC. 46 g of material was produced. The filtrate wascollected, dried in a vacuum oven, and analyzed by HPLC.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides of 2.3 81.6  7.1 0.6 2.3 0.1 — 2.1 0.2 Feed Material by HPLCwt % glycosides of 2.2 88.3  3.5 0.5 1.7 — — 1.5 — solids by HPLC wt %glycosides of 4.9 24.3 38.4 1.1 5.9 1.7 — 8.4 2.7 filtrate by HPLC

EXAMPLE 13 Example without Cooling

86 g of alcohol crystalline Steviol glycosides were placed in 190-proofethanol to produce a slurry with 19% by weight steviol glycosides. Theslurry was placed in a pressure vessel according to Example 8 at 20psig. The vessel was purged with nitrogen. The slurry was then heated to100° C. over 1 hour and held at 100° C. for 2 hours without coolingwater flowing through the cooling loop. The vessel was agitated at 180rpm. The mixture was then cooled to 70° C., filtered at 70° C., andwashed with 216 g of pure ethanol. The solids were collected andanalyzed by HPLC. 75 g of material was produced. The filtrate wascollected and dried and analyzed by HPLC.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides of 1.9 95.8 — 0.1 0.1 — —  0.9 — Feed Material by HPLC wt %glycosides of 1.5 97.1 — 0.1 — — —  0.4 — solids by HPLC wt % glycosidesof 6.4 63.8 1.7 0.8 — 0.1 — 18.8 — filtrate by HPLC

EXAMPLE 14 Example with Cooling

86 g of alcohol crystalline Steviol glycosides were placed in 190-proofethanol to produce a slurry with 19% by weight steviol glycosides. Theslurry was placed in a pressure vessel according to Example 8 at 20psig. The vessel was purged with nitrogen. The slurry was then heated to100° C. over 1 hour and held at 100° C. for two hours with flow of 60ml/min of water at 15° C. inlet through the cooling loop. The outlettemp of the cooling water was 25° C. The vessel was agitated at 180 rpm.The mixture was then cooled to 70° C., filtered at 70° C., and washedwith 216 g of pure ethanol. The solids were collected and analyzed byHPLC. 75 g of material was produced. The filtrate was collected anddried and analyzed by HPLC.

Sample Name Reb D Reb A Stev. Reb F Reb C Dulc. A Rub. Reb B StevB wt %glycosides of 1.9 95.8 — 0.1 0.1 — —  0.9 — Feed Material by HPLC wt %glycosides of 1.0 97.8 — 0.1 — — —  0.3 — solids by HPLC wt % glycosidesof 7.2 67.4 1.3 0.9 0.2 0.1 — 15.7 — filtrate by HPLC

Other embodiments of this invention will be apparent to those skilled inthe art upon consideration of this specification or from practice of theinvention disclosed herein. Various omissions, modifications, andchanges to the principles and embodiments described herein may be madeby one skilled in the art without departing from the true scope andspirit of the invention which is indicated by the following claims. Allpatents, patent documents, and publications cited herein are herebyincorporated by reference as if individually incorporated.

1-62. (canceled)
 63. A method of treating a glycoside mixture comprisingrebaudioside A material and at least one of rebaudioside B material orrebaudioside D material to help recover at least one of rebaudioside Amaterial, rebaudioside B material or rebaudioside D material in morepure form, comprising the steps of: a) providing a slurry comprisingglycosides including at least rebaudioside A material and at least oneof rebaudioside B material and rebaudioside D material, wherein theslurry includes a solid phase and a liquid phase; b) aging the slurry atone or more elevated temperatures independently greater than about 40°C., said aging occulting for a time period sufficient for the solidphase to become more pure with respect to at least one of therebaudioside A material, rebaudioside B material and rebaudioside Dmaterial; c) filtering the heated mixture to separate the solid andliquid phases, wherein the mixture is at a temperature of at least 40°C. during at least a portion of the filtering; and d) recovering atleast one glycoside in at least one of the solid and liquid phases. 64.The method of claim 63, wherein step (d) comprises recovering a solidphase comprising rebaudioside A material.
 65. The method of claim 63,wherein step (d) comprises recovering a liquid phase comprising at leastone of rebaudioside B material and rebaudioside D material.
 66. Themethod of claim 65, further comprising the step of processing the liquidphase to recover a solid phase containing at least one of rebaudioside Bmaterial and rebaudioside D material.
 67. The method of claim 63,wherein the slurry provided in step (a) includes from about 20 weightpercent to about 96 weight percent of rebaudioside A material.
 68. Themethod of claim 63, wherein the slurry provided in step (a) includes atleast about 3 weight percent total of rebaudioside B material andrebaudioside D material.
 69. The method of claim 63, wherein the slurryprovided in step (a) includes at least about 6 weight percent total ofrebaudioside B material and rebaudioside D material.
 70. The method ofclaim 63, wherein the slurry is treated in step (b) under conditionssuch that the solid phase resulting from step (c) includes at least 80weight percent rebaudioside A material.
 71. The method of claim 63,wherein the slurry is treated in step (b) under conditions such that thesolid phase resulting from step (c) includes at least 90 weight percentrebaudioside A material.
 72. The method of claim 63, wherein the slurryis treated in step (b) under conditions such that the solid phaseresulting from step (c) includes at least 96 weight percent rebaudiosideA material.
 73. The method of claim 63, wherein the slurry is treated instep (b) under conditions such that the solid phase resulting from step(c) comprises a crystalline phase that includes up to about 3 weightpercent total rebaudioside B material and rebaudioside D material. 74.The method of claim 63, wherein the liquid phase in at least one ofsteps (a) through (d) comprises at least one alcohol.
 75. The method ofclaim 74, wherein the alcohol is an aqueous alcohol.
 76. The method ofclaim 63, wherein the liquid phase in at least one of steps (a) through(d) comprises an alcohol selected from ethanol, isopropanol, methanol,n-butanol, and combinations thereof.
 77. The method of claim 76, whereinthe alcohol is an aqueous alcohol.
 78. The method of claim 63, whereinthe liquid phase in at least one of steps (a) through (d) compriseswater.
 79. The method of claim 63, wherein the slurry provided in step(a) comprises an alcohol crystalline form of at least one ofrebaudioside A material, rebaudioside B material, and rebaudioside Dmaterial.
 80. The method of claim 63, wherein aging occurs at atemperature of at least about 50° C.
 81. The method of claim 63, whereinaging occurs at a temperature of at least about 70° C.
 82. The method ofclaim 63, wherein aging occurs at a temperature of at least about 70° C.and a pressure greater than ambient pressure.
 83. The method of claim63, wherein aging occurs at an absolute pressure in the range from about1.1 atm to about 30 atm.
 84. The method of claim 63, wherein agingoccurs at an absolute pressure in the range from about 1.1 atm to about10 atm.
 85. The method of claim 63, wherein aging occurs at an absolutepressure in the range from about 1.1 atm to about 5 atm.
 86. The methodof claim 63, wherein aging occurs with mixing in the presence of acooling surface that is at a temperature less than the bulk temperatureof the mixture.
 87. The method of claim 86, wherein at least a portionof the cooling surface is at a temperature of under about 40° C.